The present invention relates to a single lens reflex camera having an autofocusing function.
More particularly, the invention relates to a camera comprising a mirror control device for moving mirrors into and out of an image-forming optical path extending from an objective lens to a film, the mirrors acting to reflect a bundle of rays transmitted from a photographic object to a finder optical system; a focus detecting device for calculating a deviation of the objective lens from an in-focus position with respect to the object; a lens drive device operable in response to the deviation detected by the focus detecting device for moving the lens to the in-focus position; and a focusing mode switching device for switching between a moving object focusing mode for permitting the lens drive device to move the lens while the mirrors are retracted from the image-forming optical path, and a stationary object focusing mode for prohibiting the lens movement during the mirror retraction. In the moving object focusing mode, the in-focus position at a photographing time is predicted and the lens movement to the predicted in-focus position is permitted concurrently with retraction of the mirrors from the image-forming optical path, thereby reducing the time taken from the start of an autofocusing operation till exposure onto the film. Hereinafter the moving object focusing mode is called a prediction focusing mode. In this mode, the focusing operation is capable of following a moving object effectively. In the stationary object focusing mode, the lens movement is prohibited during the mirror retraction, thus fixing the lens position once it has reached a focusing range adjacent an in-focus position with respect to the object. Hereinafter the stationary object focusing mode is called a one-shot focusing mode. This mode effectively prevents the lens from inadvertently deviating from the in-focus condition. Further, this construction allows the photographer to carry out what is known as focus lock photography in which a desired composition is selected by positioning the object in a photographic range different from the range corresponding to a focus detecting region after the in-focus condition is attained.
In a known camera as noted above, a control device is provided specially for switching between the prediction focusing mode and the one-shot focusing mode. The photographer manually operates this control device in accordance with his or her judgment as to photographic conditions.
With the known camera, however, since the mode switching is manually effected, the photographer could forget to carry out the switching operation or mishandle the operation, thereby establishing a wrong focusing mode. Consequently, the one-shot focusing mode may be in operation when photographing a moving object. Then the photograph is likely to be blurred since the autofocusing operation lacks reliable follow-up. Conversely, the prediction focusing mode may be selected when photographing a stationary object. When the above-mentioned focus lock photography is carried out in this state, a change in the composition will result in the focusing operation being effected with respect to an unintended object lying in the photographic range corresponding the focus detecting range after the change in the composition. The photograph thus taken will be completely out of focus.